1. Field of the Invention
The present invention relates to a new charge-transporting polymer useful for various organic electronic devices such as an electrophotographic photoconductor, a photoelectric transducer, and an organic transistor.
2. Description of the Related Art
A charge-transporting polymer, a typical example of which is polyvinylcarbazole (PVK), is useful for a photoconductive material of an electrophotographic photoconductor, a photoelectric transducer, an organic transistor material and the like. This is made into a layer and the layer is used as a charge-transporting material. As the charge-transporting material, charge-transporting polymers, a typical example of which is PVK, and low molecular weight compound dispersed systems, in which a charge-transporting low molecular weight compound is dispersed in a polymer, are well known. The low molecular weight dispersed systems are mainly used, particularly for electrophotographic photoconductors since the systems are variable in raw material thereof and can easily give high function. In recent years, electrophotographic photoconductors have been used in high-speed copiers or printers as the performance of organic photoconductors has been becoming higher. However, the performance is not insufficient at present, and the lifespan thereof is earnestly required to be longer. About the charge-transporting layer of the low molecular weight systems, which are mainstream at present, the electric properties thereof are being sufficiently satisfied. However, the charge-transporting layer has a problem that the layer is essentially poor in mechanical strength and is weak against abrasion since a low molecular weight compound is dispersed in a polymer.
On the other hand, charge-transporting polymers are actively researched at present since the polymers have possibility that the above-mentioned drawbacks are sufficiently overcome. For example, U.S. Pat. No. 4,806,443 discloses a polycarbonate obtained by polymerizing a specific dihydroxyarylamine and bischloroformate, and U.S. Pat. No. 4,806,444 discloses a polycarbonate obtained by polymerizing a specific dihydroxyarylamine and phosgene. Moreover, U.S. Pat. No. 4,801,517 discloses a polycarbonate obtained by polymerizing bishydroxyalkylarylamine, and bischloroformate or phosgene, and U.S. Pat. No. 4,937,165 and No. 4,959,228 disclose a polycarbonate obtained by polymerizing a specific dihydroxyarylamine or bishydroxyalkylarylamine, bishydroxyalkylamine, and bischloroformate, or a polyester obtained by polymerizing the amine and bisacylhalide. Furthermore, U.S. Pat. No. 5,034,296 discloses a polyester, or a polycarbonate of an arylamine having a specific fluorene skeleton, and U.S. Pat. No. 4,983,482 discloses a polyurethane. Additionally, Japanese Patent Application Publication (JP-B) No. 59-28903 discloses a polyester having, as a main chain, a specific bisstyrylbisarylamine. Japanese Patent Application Laid-Open (JP-A) Nos. 61-20953, 1-134456, 1-134457, 1-134462, 4-133065 and 4-133066 suggest polymers and photoconductors having, as a pendant, a charge-transporting substituent such as hydrazone and triarylamine.
Various properties such as solubility, film-formability, mobility, heat resistance, and matching of oxidation potential are required for a charge-transporting polymer. In order to satisfy these requirements, it is general to introduce a substituent to the polymer so as to control the physical properties thereof. Since the physical properties of the charge-transporting polymer have a correlation with physical properties of a charge-transporting monomer, which is the starting material of the polymer, the molecular design of the charge-transporting monomer becomes important.
The monomer which is the starting material of the above-mentioned triarylamine polymer can be roughly classified into two kinds, that is, (1) dihydroxyarylamine, and (2) bishydroxyalkylarylamine. However, dihydroxyarylamine has an aminophenolic structure to be easily oxidized and is not easily purified. Particularly in the case in which dihydroxyarylamine has the hydroxy group at para position, the dihydroxyarylamine becomes more unstable. Additionally, dihydroxyarylamine has a structure in which oxygen of the substituent bonds directly to the aromatic ring; therefore, charge distribution is easily unbalanced by the electron-withdrawing property of the oxygen. As a result, a problem that the mobility thereof falls easily arises.
On the other hand, bishydroxyalkylarylamine is not affected strongly by the electron-withdrawing property of oxygen because of the methylene group, but is not easily synthesized. That is, according to a reaction of diarylamine or diarylbenzidine with 3-bromoiodobenzene, a mixture tends to be produced since both of bromine and iodine have reactivity. Thus, the yield of the target amine falls. There also arises the following problem: alkyllithium, which is used when lithium is bonded to a bromine, or ethylene oxide is highly dangerous and toxic and it is therefore necessary to take notice of the handling thereof.
Accordingly, it is desirable to develop a charge-transporting material which is easily synthesized and has a high charge transportability and a superior endurance in order to develop an organic electronic device such as an electrophotographic photoconductor which is more superior in light response speed and mechanical endurance or a high-performance organic transistor.